The present invention relates to igniter devices for combustion apparatus, and more particularly to igniter devices for use in gas turbine systems.
Igniter devices of the type for use in gas turbines must be capable of igniting a combustion process within a chamber containing a combustible mixture. These devices typically accomplish this function by producing an electrical spark across a gap formed between oppositely charged electrodes of the igniter device. The spark so produced is sufficient to ignite the combustible mixture present in the combustion chamber.
In U.S. patent application Ser. No. 8,935 filed Feb. 2, 1979 by T. D. Farrell and of common assignee, an improved spark plug piston assembly is described as including a unitary conductive shell into which the internal igniter components are removably breech-loaded and assembled in an arrangement in which the internal components are protected over their entire length from the compressor discharge pressures and hot combustion products in the combustion chamber. Additionally, the internal components are retained in a predetermined position by means of a series of abutments and cooperating cylindrical retaining and insulating sleeves. Additionally, an end coupling engaged with the unitary shell removably secures the sleeves in their predetermined operative positions.
Igniter devices of the type described in the above referenced application are retractably mounted in a protective cylinder which under compressor discharge pressure cause the spark plug to retract into the protective cylinder. Typically, the igniter device is held in its fully extended position by a spring which is compressed during the retraction stroke. Unfortunately, with prior art igniters, the fully compressed length of the spring limits the extent of retraction. As a result, the size of the ignition device is greatly influenced by the fully compressed length of the spring.
Accordingly, an object of the present invention is to provide an improved retractable igniter having a greater stroke for retraction of the igniter from the hot combustion region and in which the retraction stroke is not limited by the compressed length of the spring.
It is yet another object of this invention to provide an improved igniter device with substantially the same physical dimensions but with approximately twice the stroke length of the prior art device.